Power supply topology to reduce the effects of supply pumping

Abstract

A circuit is described for balancing a power supply having a positive bus with a positive voltage, and a negative bus with a negative voltage. The circuit includes a transformer having a primary winding and a secondary winding. Switching circuitry alternately connects the positive bus and the negative bus to the primary winding of the transformer thereby generating a secondary voltage of opposite polarity on the secondary winding of the transformer. Recycling circuitry is also included which is coupled to the secondary winding of the transformer and the positive and negative buses. When the secondary voltage is greater than the positive voltage, power is transferred from the negative bus to the positive bus via the transformer and the recycling circuit. When the secondary voltage is less than the negative voltage, power is transferred from the positive bus to the negative bus via the transformer and the recycling circuit.

What is claimed is:  
     
       1. A circuit for balancing a power supply having a positive bus with a positive voltage, and a negative bus with a negative voltage, the circuit comprising: 
       a transformer having a primary winding and a first secondary winding; and  
       switching circuitry for alternately connecting the positive bus and the negative bus to the primary winding of the transformer, a primary voltage being generated on the primary winding in response thereto, a secondary voltage opposite in polarity to the primary voltage being generated on the first secondary winding in response to the primary voltage; and  
       recycling circuitry coupled to the first secondary and the positive and negative buses;  
       wherein when the secondary voltage is greater than the positive voltage, power is transferred from the negative bus to the positive bus via the transformer and the recycling circuitry, and when the secondary voltage is less than the negative voltage, power is transferred from the positive bus to the negative bus via the transformer and the recycling circuitry.  
     
     
       2. The circuit of claim  1  wherein the transformer further comprises a second secondary winding and wherein the circuit further comprises bias supply circuitry coupled to the second secondary for generating a bias voltage. 
     
     
       3. The circuit of claim  1  wherein the transformer further comprises a second secondary winding for generating a feedback signal, the feedback signal being for use by a power supply controller in the power supply. 
     
     
       4. The circuit of claim  1  wherein the switching circuitry comprises first and second switches connected in series between the positive bus and the negative bus. 
     
     
       5. The circuit of claim  4  wherein the first and second switches comprise MOSFETs. 
     
     
       6. The circuit of claim  4  further comprising gate drive circuitry for operating the first and second switches. 
     
     
       7. The circuit of claim  6  wherein the gate drive circuitry is operable to drive the first and second switches with alternating 50% duty cycles. 
     
     
       8. The circuit of claim  6  wherein the gate drive circuitry comprises second and third secondaries coupled to a gate drive transformer in the power supply. 
     
     
       9. The circuit of claim  1  wherein the recycling circuitry comprises first and second diodes connected in series between the positive bus and the negative bus, the secondary winding being coupled to the first and second diodes, wherein when the secondary voltage is greater than the positive voltage, power is transferred from the negative bus to the positive bus via the transformer and the first diode, and when the secondary voltage is less than the negative voltage, power is transferred from the positive bus to the negative bus via the transformer and the second diode. 
     
     
       10. A circuit for balancing a power supply having a positive bus with a positive voltage, and a negative bus with a negative voltage, the circuit comprising: 
       first and second switches connected in series between the positive bus and the negative bus;  
       first and second diodes connected in series between the positive bus and the negative bus;  
       a transformer having a primary winding and a secondary winding, the primary winding being coupled to the first and second switches, the secondary winding being coupled to the first and second diodes;  
       balancing circuitry for alternately turning the first and second switches on, and alternately connecting the positive bus and the negative bus of the power supply to the primary winding of the transformer, a primary voltage being generated on the primary winding in response thereto, a secondary voltage opposite in polarity to the primary voltage being generated on the secondary winding in response to the primary voltage;  
       wherein when the secondary voltage is greater than the positive voltage, power is transferred from the negative bus to the positive bus via the transformer and the first diode, and when the secondary voltage is less than the negative voltage, power is transferred from the positive bus to the negative bus via the transformer and the second diode.  
     
     
       11. A circuit for balancing a power supply having a positive bus with a positive voltage, and a negative bus with a negative voltage, the circuit comprising: 
       means for alternately connecting the positive bus and the negative bus to a primary winding of a transformer, a primary voltage being generated on the primary winding in response thereto, a secondary voltage opposite in polarity to the primary voltage being generated on a secondary winding in response to the primary voltage;  
       means for transferring power from the negative bus to the positive bus where the secondary voltage is greater than the positive voltage; and  
       means for transferring power from the positive bus to the negative bus where the secondary voltage is less than the negative voltage.  
     
     
       12. A power supply, comprising: 
       a positive bus with a positive voltage;  
       a negative bus with a negative voltage; and  
       a circuit for balancing the positive and negative voltages, the circuit comprising:  
       a transformer having a primary winding and a secondary winding;  
       switching circuitry for alternately connecting the positive bus and the negative bus to the primary winding of the transformer, a primary voltage being generated on the primary winding in response thereto, a secondary voltage opposite in polarity to the primary voltage being generated on the secondary winding in response to the primary voltage; and  
       recycling circuitry coupled to the first secondary and the positive and negative buses;  
       wherein when the secondary voltage is greater than the positive voltage, power is transferred from the negative bus to the positive bus via the transformer and the recycling circuitry, and when the secondary voltage is less than the negative voltage, power is transferred from the positive bus to the negative bus via the transformer and the recycling circuitry.  
     
     
       13. A method for balancing a power supply having a positive bus with a positive voltage, and a negative bus with a negative voltage, the method comprising: 
       alternately connecting the positive bus and the negative bus to a primary winding of a transformer, a primary voltage being generated on the primary winding in response thereto, a secondary voltage opposite in polarity to the primary voltage being generated on a secondary winding in response to the primary voltage;  
       where the secondary voltage is greater than the positive voltage, transferring power from the negative bus to the positive bus via the transformer; and  
       where the secondary voltage is less than the negative voltage, transferring power from the positive bus to the negative bus via the transformer.